The “false vine” brings forth thorns instead of grapes

 John 15:1-7

In that time Jesus said to his disciples: I an the true vine; and my Father is the husbandman. And so on.

Homily by St. Augustine, Bishop of Hippo.
Tract 80 on John
Dearly beloved brethren, this passage of the Gospel, wherein the Lord saith that He is the vine, and that His disciples are the branches, is to be taken in that sense wherein it is also said, that He is the Head of the Church, Eph. v. 23, and that we are the members of Him 30 Who is the Mediator between God and men, the man Christ Jesus 1 Tim. ii. 5. The vine and his branches are of one and the same nature. Therefore, seeing that He was God, of which nature we are not, He was made man, to the end that He might have in Himself this vine, that is, the manhood, whereof we men can be made branches.

Why saith He: I am the true vine? As touching this word true, hath He not here regard to that other parable of a vine, the like figure whereto He doth here apply to Himself? Jer. ii. 21. Here is He called a vine, not plainly, but in parable, as also He is called elsewhere a sheep, Isa. liii. 7, Acts viii. 32, a lamb, John i. 36, a lion, Apoc. v. 5, a rock, 1 Cor. x. 4, a corner-stone, ~Eph. ii. 20, and other things of the like kind. But these things are in themselves that which they seem to be, albeit He is called by their names, not plainly, but in a parable, and herein are they different from that vine, whereof in this place He taketh on Him the name. For when He saith: I am the true vine, doth He not make distinction between Himself, and that which indeed seemed to be a vine, but to which it is said: How art thou turned into the degenerate plant of a strange vine unto Me? Jer. ii. 21. For by what title shall that plant be called other than a false vine, whereto they looked that she should bring forth grapes, and she brought forth thorns?